Two gauges tell the whole story of a fuel pump. Pressure at the nozzle port says what the nozzle is fed at, which sets the firing rate as much as the nozzle size does. Vacuum on the suction side says whether the line is restricted, too long, or pulling air. A tester in a case carries both with the fittings that match the pump. Bleeding through the control is on the pump prime mode page.
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A 0 to 300 psi gauge that threads into the port on the fuel pump. It reads the pressure the nozzle is fed at.
Why it earns its place: Pump pressure is the second number the nozzle chart needs. Pressure sets the firing rate as much as the nozzle does.
A gauge that reads the suction on the inlet side of the pump, in inches of mercury.
Why it earns its place: High vacuum means a restriction: a plugged filter, or a line too long or too high for one pipe. It finds the lockout that only happens on cold nights.
A pressure and vacuum test set in a case, with the adapters that fit the common fuel pump ports.
Why it earns its place: One case instead of loose gauges and fittings hunted through a drawer.
A sheet of oil-only sorbent laid under the burner, filter, and pump. It catches the drips from a filter change, a bleed, or a weeping fitting before they soak into the floor and leave the boiler room smelling of oil.
Replace it when: Whenever a pad is saturated or you can smell oil near the burner. Put a fresh one down before a filter change or a bleed, and keep a pack on the shelf.
https://oilburnerhelp.com/gear/pump-test/